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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Informational draft: draft-ietf-dart-dscp-rtp (ref. 'I-D.ietf-dart-dscp-rtp') == Outdated reference: A later version (-26) exists of draft-ietf-rtcweb-rtp-usage-25 == Outdated reference: A later version (-12) exists of draft-ietf-rtcweb-security-08 == Outdated reference: A later version (-17) exists of draft-ietf-rtcweb-transports-10 ** Downref: Normative reference to an Informational RFC: RFC 4594 Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group S. Dhesikan 3 Internet-Draft C. Jennings 4 Intended status: Standards Track Cisco Systems 5 Expires: June 20, 2016 D. Druta, Ed. 6 AT&T 7 P. Jones 8 Cisco Systems 9 December 18, 2015 11 DSCP and other packet markings for WebRTC QoS 12 draft-ietf-tsvwg-rtcweb-qos-07 14 Abstract 16 Many networks, such as service provider and enterprise networks, can 17 provide treatment for individual packets based on Differentiated 18 Services Code Point (DSCP) values on a per-hop basis. This document 19 provides the recommended DSCP values for browsers to use for various 20 classes of traffic. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on June 20, 2016. 39 Copyright Notice 41 Copyright (c) 2015 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 2. Relation to Other Standards . . . . . . . . . . . . . . . . . 3 58 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 4. Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 5. DSCP Mappings . . . . . . . . . . . . . . . . . . . . . . . . 5 61 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 62 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 63 8. Downward References . . . . . . . . . . . . . . . . . . . . . 7 64 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 65 10. Dedication . . . . . . . . . . . . . . . . . . . . . . . . . 8 66 11. Document History . . . . . . . . . . . . . . . . . . . . . . 8 67 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 68 12.1. Normative References . . . . . . . . . . . . . . . . . . 8 69 12.2. Informative References . . . . . . . . . . . . . . . . . 9 70 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 72 1. Introduction 74 Differentiated Services Code Points (DSCP) [RFC2474] style packet 75 marking can help provide QoS in some environments. There are many 76 use cases where such marking does not help, but it seldom makes 77 things worse if packets are marked appropriately. In other words, if 78 too many packets, say all audio or all audio and video, are marked 79 for a given network condition then it can prevent desirable results. 80 Either too much other traffic will be starved, or there is not enough 81 capacity for the preferentially marked packets (i.e., audio and/or 82 video). 84 This specification proposes how WebRTC applications can mark packets. 85 This specification does not contradict or redefine any advice from 86 previous IETF RFCs, but merely provides a simple set of 87 recommendations for implementers based on the previous RFCs 89 There are some environments where DSCP markings frequently help. 90 These include: 92 1. Private, wide-area networks. 94 2. Residential Networks. If the congested link is the broadband 95 uplink in a cable or DSL scenario, often residential routers/NAT 96 support preferential treatment based on DSCP. 98 3. Wireless Networks. If the congested link is a local wireless 99 network, marking may help. 101 Traditionally DSCP values have been thought of as being site 102 specific, with each site selecting its own code points for 103 controlling per-hop-behavior to influence the QoS for transport-layer 104 flows. However in the WebRTC use cases, the browsers need to set 105 them to something when there is no site specific information. In 106 this document, "browsers" is used synonymously with "Interactive User 107 Agent" as defined in the HTML specification, 108 [W3C.REC-html5-20141028]. This document describes a subset of DSCP 109 code point values drawn from existing RFCs and common usage for use 110 with WebRTC applications. These code points are solely defaults. 112 This specification defines some inputs that the browser in a WebRTC 113 application can consider to aid in determining how to set the various 114 packet markings and defines the mapping from abstract QoS policies 115 (data type, priority level) to those packet markings. 117 2. Relation to Other Standards 119 This document exists as a complement to [I-D.ietf-dart-dscp-rtp], 120 which describes the interaction between DSCP and real-time 121 communications. It covers the implications of using various DSCP 122 values, particularly focusing on Real-time Transport Protocol (RTP) 123 [RFC3550] streams that are multiplexed onto a single transport-layer 124 flow. 126 There are a number of guidelines specified in 127 [I-D.ietf-dart-dscp-rtp] that should be followed when marking traffic 128 sent by WebRTC applications, as it is common for multiple RTP streams 129 to be multiplexed on the same transport-layer flow. Generally, the 130 RTP streams would be marked with a value as appropriate from Table 1. 131 A WebRTC application might also multiplex data channel 132 [I-D.ietf-rtcweb-data-channel] traffic over the same 5-tuple as RTP 133 streams, which would also be marked as per that table. The guidance 134 in [I-D.ietf-dart-dscp-rtp] says that all data channel traffic would 135 be marked with a single value that is typically different than the 136 value(s) used for RTP streams multiplexed with the data channel 137 traffic over the same 5-tuple, assuming RTP streams are marked with a 138 value other than default forwarding (DF). This is expanded upon 139 further in the next section. 141 This specification does not change or override the advice in any 142 other standards about setting packet markings. It simply selects a 143 subset of DSCP values that is relevant in the WebRTC context. This 144 document also specifies the inputs that are needed by the browser to 145 provide to the media engine. 147 The DSCP value set by the endpoint is not always trusted by the 148 network. Therefore, the DSCP value may be remarked at any place in 149 the network for a variety of reasons to any other DSCP value, 150 including default forwarding (DF) value to provide basic best effort 151 service. The mitigation for such action is through an authorization 152 mechanism. Such authorization mechanism is outside the scope of this 153 document. There is benefit in marking traffic even if it only 154 benefits the first few hops. 156 3. Terminology 158 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 159 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 160 document are to be interpreted as described in [RFC2119]. 162 4. Inputs 164 The below uses the concept of a media flow, however this is usually 165 not equivalent to a transport-layer flow defined by a 5-tuple (source 166 address, destination address, source port, destination port, and 167 protocol). Instead each media flow, such as an RTP stream 168 [I-D.ietf-rtcweb-rtp-usage] or SCTP association carrying data channel 169 packets [I-D.ietf-rtcweb-data-channel], contains all the packets 170 associated with an independent media entity within one 5-tuple. 171 There may be multiple media flows within the same 5-tuple. These 172 media flows might consist of different media types and have different 173 levels of importance to the application and, therefore, each 174 potentially marked using different DSCP values than for another media 175 flow multiplexed over the same transport-layer flow. The following 176 are the inputs that the browser provides to the media engine: 178 o Data Type: The browser provides this input as it knows if the flow 179 is audio, interactive video with or without audio, non-interactive 180 video with or without audio, or data. 181 o Application Priority: Another input is the relative importance of 182 the flow within that data type. Many applications have multiple 183 media flows of the same data type and often some flows are more 184 important than others. For example, in a video conference where 185 there are usually audio and video flows, the audio flow may be 186 more important than the video flow. JavaScript applications can 187 tell the browser whether a particular media flow is high, medium, 188 low or very low importance to the application. 190 [I-D.ietf-rtcweb-transports] defines in more detail what an 191 individual media flow is within the WebRTC context. 193 As an example of different media flows that might be multiplexed over 194 the same transport-layer flow, packets related to one RTP stream 195 (e.g., an audio flow) carried over UDP might be one media flow, 196 packets related to a second RTP stream (e.g., presentation video) 197 carried over UDP might be a second media flow, and finally data 198 channel packets carried via SCTP over DTLS might be third media flow. 200 5. DSCP Mappings 202 Below is a table of DSCP markings for each data type of interest to 203 WebRTC. These DSCP values for each data type listed are a reasonable 204 subset of code point values taken from [RFC4594]. A web browser 205 SHOULD use these values to mark the appropriate media packets. More 206 information on EF can be found in [RFC3246]. More information on AF 207 can be found in [RFC2597]. DF is default forwarding which provides 208 the basic best effort service. 210 +------------------------+-------+------+-------------+-------------+ 211 | Data Type | Very | Low | Medium | High | 212 | | Low | | | | 213 +------------------------+-------+------+-------------+-------------+ 214 | Audio | CS1 | DF | EF (46) | EF (46) | 215 | | (8) | (0) | | | 216 | | | | | | 217 | Interactive Video with | CS1 | DF | AF42, AF43 | AF41, AF42 | 218 | or without audio | (8) | (0) | (36, 38) | (34, 36) | 219 | | | | | | 220 | Non-Interactive Video | CS1 | DF | AF32, AF33 | AF31, AF32 | 221 | with or without audio | (8) | (0) | (28, 30) | (26, 28) | 222 | | | | | | 223 | Data | CS1 | DF | AF11 | AF21 | 224 | | (8) | (0) | | | 225 +------------------------+-------+------+-------------+-------------+ 227 Table 1: Recommended DSCP Values for WebRTC Applications 229 The columns "very low", "low", "Medium" and "high" signify the 230 relative importance of the media flow within the application and is 231 an input that the browser receives to assist it in selecting the DSCP 232 value. These are referred to as application priority in this 233 document. Application priority does not refer to priority in the 234 network transport. 236 The above table assumes that packets marked with CS1 are treated as 237 "less than best effort". However, the treatment of CS1 is 238 implementation dependent. If an implementation treats CS1 as other 239 than "less than best effort", then the actual priority (or, more 240 precisely, the per-hop-behavior) of the packets may be changed from 241 what is intended. It is common for CS1 to be treated the same as DF 242 so anyone using CS1 cannot assume that CS1 will be treated 243 differently than DF. Implementers should also note that the excess 244 EF traffic is dropped. This could mean that a packet marked as EF 245 may not get through as opposed to a packet marked with a different 246 DSCP value. 248 The browser SHOULD first select the data type of the media flow. 249 Within the data type, the relative importance of the media flow 250 SHOULD be used to select the appropriate DSCP value. 252 The combination of data type and application priority provides 253 specificity and helps in selecting the right DSCP value for the media 254 flow. In some cases, the different drop precedence values provides 255 additional granularity in classifying packets within a media flow. 256 For example, in a video conference, the video media flow may have 257 medium application priority. If so, either AF42 or AF43 may be 258 selected. If the I-frames in the stream are more important than the 259 P-frames, then the I-frames can be marked with AF42 and the P-frames 260 marked with AF43. 262 All packets within a media flow SHOULD have the same application 263 priority. In some cases, the selected cell may have multiple DSCP 264 values, such as AF41 and AF42. These offer different drop 265 precedences. With the exception of data channel traffic, one may 266 select different drop precedences for the different packets in the 267 same media flow. Therefore, all packets in the media flow SHOULD be 268 marked with the same application priority, but can have different 269 drop precedences. 271 For reasons discussed in Section 6 of [I-D.ietf-dart-dscp-rtp], if 272 multiple media flows are multiplexed using a reliable transport 273 (e.g., TCP) then all of the packets for all media flows multiplexed 274 over that transport-layer flow MUST be marked using the same DSCP 275 value. Likewise, all WebRTC data channel packets transmitted over an 276 SCTP association MUST be marked using the same DSCP value, regardless 277 of how many data channels (streams) exist or what kind of traffic is 278 carried over the various SCTP streams. In the event that the browser 279 wishes to change the DSCP value in use for an SCTP association, it 280 MUST reset the SCTP congestion controller after changing values. 281 Frequent changes in the DSCP value used for an SCTP association are 282 discouraged, though, as this would defeat any attempts at effectively 283 managing congestion. It should also be noted that any change in DSCP 284 value that results in a reset of the congestion controller puts the 285 SCTP association back into slow start, which may have undesirable 286 effects on application performance. 288 For the data channel traffic multiplexed over an SCTP association, it 289 is RECOMMENDED that the DSCP value selected be the one associated 290 with the highest priority requested for all data channels multiplexed 291 over the SCTP association. Likewise, when multiplexing multiple 292 media flows over a TCP connection, the DCSP value selected should be 293 the one associated with the highest priority requested for all 294 multiplexed flows. 296 If a packet enters a QoS domain that has no support for the above 297 defined data types/application priority (service class), then the 298 network node at the edge will remark the DSCP value based on 299 policies. This could result in the media flow not getting the 300 network treatment it expects based on the original DSCP value in the 301 packet. Subsequently, if the packet enters a QoS domain that 302 supports a larger number of service classes, there may not be 303 sufficient information in the packet to restore the original 304 markings. Mechanisms for restoring such original DSCP is outside the 305 scope of this document. 307 In summary, there are no guarantees or promised level of service with 308 the use of DSCP. The service provided to a packet is dependent upon 309 the network design along the path, as well as the congestion levels 310 at every hop. 312 6. Security Considerations 314 This specification does not add any additional security implication 315 other than the normal application use of DSCP. For security 316 implications on use of DSCP, please refer to Section 6 of RFC 4594. 317 Please also see [I-D.ietf-rtcweb-security] as an additional 318 reference. 320 7. IANA Considerations 322 This specification does not require any actions from IANA. 324 8. Downward References 326 This specification contains a downwards reference to [RFC4594]. 327 However, the parts of that RFC used by this specification are 328 sufficiently stable for this downward reference. 330 9. Acknowledgements 332 Thanks To David Black, Magnus Westerland, Paolo Severini, Jim 333 Hasselbrook, Joe Marcus, Erik Nordmark, and Michael Tuexen for their 334 help. 336 10. Dedication 338 This document is dedicated to the memory of James Polk, a long-time 339 friend and colleague. James made important contributions to this 340 specification, including being one of its primary authors. The IETF 341 global community mourns his loss and he will be missed dearly. 343 11. Document History 345 Note to RFC Editor: Please remove this section. 347 This document was originally an individual submission in RTCWeb WG. 348 The RTCWeb working group selected it to be become a WG document. 349 Later the transport ADs requested that this be moved to the TSVWG WG 350 as that seemed to be a better match. This document is now being 351 submitted as individual submission to the TSVWG with the hope that WG 352 will select it as a WG draft and move it forward to an RFC. 354 12. References 356 12.1. Normative References 358 [I-D.ietf-dart-dscp-rtp] 359 Black, D. and P. Jones, "Differentiated Services 360 (DiffServ) and Real-time Communication", draft-ietf-dart- 361 dscp-rtp-10 (work in progress), November 2014. 363 [I-D.ietf-rtcweb-data-channel] 364 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data 365 Channels", draft-ietf-rtcweb-data-channel-13 (work in 366 progress), January 2015. 368 [I-D.ietf-rtcweb-rtp-usage] 369 Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time 370 Communication (WebRTC): Media Transport and Use of RTP", 371 draft-ietf-rtcweb-rtp-usage-25 (work in progress), June 372 2015. 374 [I-D.ietf-rtcweb-security] 375 Rescorla, E., "Security Considerations for WebRTC", draft- 376 ietf-rtcweb-security-08 (work in progress), February 2015. 378 [I-D.ietf-rtcweb-transports] 379 Alvestrand, H., "Transports for WebRTC", draft-ietf- 380 rtcweb-transports-10 (work in progress), October 2015. 382 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 383 Requirement Levels", BCP 14, RFC 2119, March 1997. 385 [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration 386 Guidelines for DiffServ Service Classes", RFC 4594, August 387 2006. 389 12.2. Informative References 391 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 392 "Definition of the Differentiated Services Field (DS 393 Field) in the IPv4 and IPv6 Headers", RFC 2474, December 394 1998. 396 [RFC2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski, 397 "Assured Forwarding PHB Group", RFC 2597, June 1999. 399 [RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec, 400 J., Courtney, W., Davari, S., Firoiu, V., and D. 401 Stiliadis, "An Expedited Forwarding PHB (Per-Hop 402 Behavior)", RFC 3246, March 2002. 404 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 405 Jacobson, "RTP: A Transport Protocol for Real-Time 406 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 407 July 2003, . 409 [W3C.REC-html5-20141028] 410 Hickson, I., Berjon, R., Faulkner, S., Leithead, T., 411 Navara, E., O'Connor, E., and S. Pfeiffer, "HTML5", 412 World Wide Web Consortium Recommendation REC- 413 html5-20141028, October 2014, 414 . 416 Authors' Addresses 418 Subha Dhesikan 419 Cisco Systems 421 Email: sdhesika@cisco.com 423 Cullen Jennings 424 Cisco Systems 426 Email: fluffy@cisco.com 427 Dan Druta (editor) 428 AT&T 430 Email: dd5826@att.com 432 Paul E. Jones 433 Cisco Systems 435 Email: paulej@packetizer.com